Problem: $ E = \left[\begin{array}{rrr}-1 & 1 & 3 \\ 4 & 3 & 1 \\ -1 & 1 & 2 \\ 1 & -2 & 0\end{array}\right]$ What are the dimensions of matrix $ E$ ?
Explanation: The first dimension is the number of rows in the matrix. How many rows does $ E$ have? The second dimension is the number of columns in the matrix. How many columns does $ E$ have? So, $ E$ is a 4 $\times$ 3 matrix.